1. Technical Field
The invention relates to turbomachines, like those used for aircraft propulsion, and particularly the ring support spacer for the high pressure turbine and its assembly with minimized clearances.
2. Prior Art and Problem that Arises
With reference to FIG. 1, as described in patent document EP-0 555 082, in many different turbomachines, the turbine casing 1 of the stator comprises annular parts 2 facing the blades 3 of the rotor 8, at the inlet to the high pressure turbine on the output side of the combustion chamber 5. Therefore these annular parts 2 of the turbine casing 1 define a clearance with the end of the blades 3 of the rotor 4, and consequently control the efficiency of the turbomachine.
These annular parts 2 are supplied with gas at temperatures that can either expand them or contract them to minimize the actual clearance between these blades 3 and these annular parts 4, in order to increase the efficiency of the turbomachine. The gas is usually drawn off from another part of the turbomachine as a function of the gas temperature or the rotor speed.
FIG. 2 shows the details of an embodiment according to prior art of the attachment of a stator ring 2 around the ends of the blades 3 of the rotor 4. A ring is composed of a large number of ring sectors 2, each positioned in support spacer sectors 4 that are themselves fixed to the inside of the casing 1 of the high pressure turbine. Consequently, each support spacer sector 4 has an upstream outer foot 6M and a downstream outer foot 6V that will be inserted in a corresponding upstream hook 7M or downstream hook 7V on the high pressure turbine casing 1. It is found that a clearance J has to be allowed between the ends of the blades 3 and the wall of each ring sector 2. The temperature differences between the rest and operating positions at these elements are very large for this type of turbomachine. The result is various expansions in three dimensions at different scales on the parts forming part of this assembly. Obviously, if the clearance J remains significant, particularly during the operating phases of the turbomachine, the efficiency of the turbine will be very much reduced.
Document EP-0 555 082 also describes an assembly process by tightening the spacer or the suspension element of each ring sector in the high pressure turbine.
FIG. 3 illustrates the placement of a support spacer 4 with two ends 4A and 4B and a median part 4C, represented superposed on a part of the high pressure turbine casing 1 and its upstream hook 7M and downstream hook 7V. The high pressure turbine casing 1 comprises a first radius R1 and a first width X1. The support spacer sector 4 comprises a second radius R2 and a second width X2. The second radius R2 is offset from the first radius R1, such that the second radius R2 is larger than the first radius R1. Furthermore, the first width X1 is preferably greater than the second width X2. The support spacer sector 4 is force fitted into the slit formed by the hooks 7M and 7V and the high pressure turbine casing 1. This force fitted assembly creates a spring effect in the support spacer sector 4 due to the deformation or deflection of the ends 4A and 4B of this support spacer sector 4 as shown in FIG. 4.
Due to the radial temperature gradients at this level, these support spacer sectors 4 are subject to deformations, particularly concerning their camber. Considering the fact that the hot fibers are located towards the inside of the compressor and the cold fibers are towards the outside of the compressor, the support spacer sectors tend to see their camber angle R2 increase, which increases bending. Furthermore, the large number of successive flight cycles undergone by this type of turbomachine means that these elements reach high temperatures very many times and therefore the geometry of these parts varies from their initial geometry. This makes it more difficult to compensate for clearances. The clearance J between the ends of the blades and the turbine ring increases, reducing the efficiency of the turbomachine.
Therefore, the purpose of the invention is to propose another solution to compensate for the clearances between the ends of the rotor blades and the ring sectors at the high pressure turbine, by attempting to prevent deformations due to radial temperature gradients.
Consequently, the main purpose of the invention is a support spacer sector for the ring of the high pressure turbine in a turbomachine with compensation for spacer sector assembly clearances and functional clearances between the ring and the end of the blades, this sector comprising:
an upstream radial wall with an external upstream hook that will be axially engaged in an corresponding upstream notch on the high pressure casing of the turbomachine and a internal upstream hook that will be engaged in a corresponding notch in the ring;
a downstream radial wall with an external downstream hook that will be axially engaged in an corresponding downstream hook on the high pressure casing of the turbomachine and an internal downstream hook that will fit into the corresponding ring sector;
an upstream longitudinal tab fixed on the upstream side and the outside of the upstream radial wall with an outside thrust face at its upstream end, acting as a projection towards the outside, so that it is in contact on the inside of the casing of the high pressure turbine of the turbomachine and exerts pressure on it when the support spacer sector is in place.
According to the invention with the tab fixed on the upstream side of the upstream wall, the radial thrust surface of the end of the upstream tab is not continuous but is separated by recesses such that gases can pass through.
In the preferred embodiment of the spacer sector, a positioning notch is provided on the upstream end in which a rotation indexing pin can be fitted, penetrating into a hole in the high pressure casing of the turbomachine.
It is preferable that the outside recesses at the end of the upstream wall are not as deep as the length that projects through the indexing pin to form an angular foolproofing means when setting up the assembly.